linux-kernel - Re: [PATCH v2 2/5] mm: zswap: calculate limits only when updated

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Date: Tue, 9 Apr 2024 17:52:59 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Nhat Pham <nphamcs@...il.com>, Chengming Zhou <chengming.zhou@...ux.dev>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] mm: zswap: calculate limits only when updated

[..]
> > Do we need a separate notifier chain for totalram_pages() updates?
>
> Good question. I actually might have the requirement to notify some arch
> code (s390x) from virtio-mem when fake adding/removing memory, and
> already wondered how to best wire that up.
>
> Maybe we can squeeze that into the existing notifier chain, but needs a
> bit of thought.

Do you mean by adding new actions (e.g. MEM_FAKE_ONLINE,
MEM_FAKE_OFFLINE), or by reusing the existing actions (MEM_ONLINE,
MEM_OFFLINE, etc).

New actions mean minimal impact to existing notifiers, but it may make
more sense to reuse MEM_ONLINE and MEM_OFFLINE to have generic actions
that mean "memory increased" and "memory decreased".

I suppose we can add new actions and then separately (and probably
incrementally) audit existing notifiers to check if they want to
handle the new actions as well.

Another consideration is that apparently some ballooning drivers also
register notifiers, so we need to make sure there is no possibility of
deadlock/recursion.